Zinc cyanide plating bath



United States Patent 3,168,453 ZINC CYANIDE PLATING BATH Anthony Debe,18203 Canterbury Road, Cleveland, Ohio No Drawing. Filed June 28, 1961,Ser. No. 120,208 14 Claims. (Cl. 204-44) The present invention isdirected to an improved alkaline cyanide plating bath and the method ofmaking the same. The invention is particularly directed to the use of acatalytic ingredient in alkaline cyanide plating baths for theelectrolytic deposition of zinc and zinc alloys such as copper-zincalloys.

It is an object of the present invention to provide an improved alkalinecyanide plating bath for the electrolytic deposition of zinc and zincalloys in which a catalytic ingredient comprising a reaction product ofhexamethylene tetramine and salicylic acid is used.

It is an object of the present invention to provide an improved platingbath and a method of making the same in which zinc and zinc alloys aredeposited electrolytically from the bath, the bath containing an anodecorroder and a smoothing and grain refining agent.

It is an object of the present invention to provide an improved alkalinecyanide plating bath and the method of making the same in which acatalytic ingredient is used, the catalytic ingredient being an anodecorroder as well as a smoothing and grain refining agent.

It is an object of the present invention to provide an improved aqueousalkaline cyanide plating bath comprising a zinc or zinc alloy cyanide,an alkali metal hydroxide, an alkali metal cyanide, an alkali metaltartrate, and a reaction product of salicylic acid and hexamethylenetetramine.

These and other objects will be apparent from the specification thatfollows and from the appended claims.

The present invention provides an aqueous alkaline cyanide plating bathin which a reaction product of salicylic acid and hexamethylenetetramine (also called hexamine) is used as an anode corroder and asmoothing and grain refining agent for the electrolytic deposition ofzinc and zinc alloys. In accordance with the present invention, theplating bath deposits a fine grained, smooth coating in which anysandpaper effect is eliminated or reduced substantially and in which thecathode performance is improved.

The amount of smoothing and grain refining agent generally used toobtain the above improvement may be in the range of about 0.1 to 7.0ounces per gallon (or about 0.75 to 53 grams per liter) of the reactionproduct of salicylic acid and hexamine-although, for best results, it ispreferred that at least about 0.4 ounce and up to as high as about 4ounces per gallon or more, sometimes even as high as 6 ounces, of theabove described smoothing agent be used.

Suitable plating bath formulations, including the general ranges andpreferred ranges of the above described reaction product used as ananode corroder and a smoothing and grain refining agent, are set forthbelow in Table 1.

As it will hereinafter be described in detail, the above describedsmoothing and grain refining agent or reaction product is an alkalinesolution made by reacting hexamine and salicylic acid at pH of 2 /2 to/2 and thereafter further reacting the acidic reaction product with analkali hydroxide to provide the final solution. Thus, the final solutioncontains amino derivatives (apparently ortho and para) of salicylic acidand hexamine as well as unreacted starting ingredients, etc., which actas buffers and the like to aid the catalytic activity of the aminoderivatives.

As previously indicated, the above described amino derivativesapparently provide most of the catalytic activity and, thus, may beconsidered the catalytic ingredient. The amino derivatives, as thecatalytic agent, are generally present in an amount of about 0.9% toabout 67% by weight of the total alkaline solution used as the smoothingand grain refining agent. Thus, the amino derivatives are generallypresent in the range about 0.0009 to 4.7 ounces per gallon (or about 0.6to 35 grams per liter) of the plating bath. The preferred range for theamino derivatives, as previously indicated for the final alkalinesolution, is about 0.1 to 1 ounce per gallon. As seen from the abovediscussion, it is possible, according to the present invention, toprovide a concentrated solution of the above described amino derivativesand add other materials such as tartrates and alkali metal hydroxides toprovide an alkaline solution for use as a smoothing and grain refiningagent as well as an anode corroder. In any event however, the totalamount of amino derivatives of salicylic acid must be Within the abovedescribed amounts to have an effective plating bath additive.

In accordance with the present invention, the cyanide (as indicated inTable 1) may be zinc cyanide or a combination of zinc and coppercyanide, the combination being used to deposit a zinc-copper alloy, thezinc cyanide salt preferably being a substantial portion say, about atleast 10% of the metal cyanide content. While the alkali hydroxide maybe potassium hydroxide, is preferred that sodium hydroxide be used asindicated in Table 1.

As to the alkali cyanide, it is highly preferred that potassium cyanidebe used although sodium cyanide can be used. As indicated above thealkali cyanide is preferably used in amounts as low as 5 or 10 oz. pergal. up to about 15 oz. per gal.

Returning to the reaction product of salicylic acid and hexamine whichhas been found to be an outstanding anode corroder as well as anexcellent smoothing and grain refining agent, the reaction product ispreferably made by reacting the hexamine and salicylic acid at about upto as high as F. to F. in an aqueous solution. However, generally about125 to F. may be employed as the reaction temperature range to obtain auseful product. Also a pH of about 2 /2 to 5 /2 and preferably about 4.2to 4.8 must be used with the above temperature range to obtain acommercially useful prodnot.

The reaction time should be at least 4 hours, and, better, at least 8hours. In general, the time of reaction may be varied between 8 to 72hours, the best catalytic ingredient solution being usually obtainedwith a reaction time of about 20 to 40 hours.

During the reaction, the amount of each of the ingredients used isimportant. Generally, the reaction is made by reacting about one mole ofhexamine with about 1 to 4 moles of salicyclic acid to provide sufncientamino derivatives although it is preferred that about 2 /2 up to as highas about 3% to 3 /2 moles of salicyclic acid be used under the abovereaction conditions just described.

After the reaction has completed and all the salicylic acid has beendissolved and the gassing has ceased, an alkali metal hydroxide such assodium hydroxide and preferably potassium hydroxide should be added forfurther reaction which brings the pH of the solution up to about 8.5 to12. Again, while a pH of 12 may be employed for further reaction withthe KOH, a pH of 9 /2 or /2 up to 11 /2 is highly preferred with thebest results being obtained with a narrow pH range of about 9.8 to 10.5or slightly higher, up to about 11.6. It has been found that when the pHis about 12, the reaction product is different and is generally notacceptable as an additive for a plating bath containing copper.Likewise, a pH of 8 or less does not provide a satisfactory material,its stability not being enough to justify its use as a catalyticingredient in plating baths.

As to the amount of potassium hydroxide or other alkaline metalhydroxide added, it is preferred that around 2 /2 to 3 /2 moles ofpotassium hydroxide be used, although generally about 2% to 4 moles maybe employed in accordance with the present invention. Along with theabove amount of KOH or other alkali metal hydroxide, it is preferredthat the reaction be continued at about 70 to 190 F. for at least 4hours and preferably about 8 to 72 hours.

Thus, on the basis of 1200 lbs. of salicylic acid used as one of thestarting ingredients, generally 300 to 450 lbs. of hexamine may be used,although the preferred amount is about 380 to 420 lbs. Likewise, thepreferred amount of potassium hydroxide is about 380 to 420 lbs. Thebest results are obtained using about 400 lbs. of KOH, althoughgenerally about 300 to 500 lbs. may be used with the 1200 lbs. ofsalicyclic acid to obtain a reaction product that is usefulcommercially.

Also, in the above process, it is highly desirable to let the acidicreaction solution stand about 8 to 72 hours and preferably 16 to 32hours before further reacting the solution with the potassium hydroxide.

While adding the potassium hydroxide in accordance with the presentinvention, it is also preferred that about 1 to 3 moles of an alkalinemetal salt of tartaric acid be used, the preferred additive beingpotassium tartrate although sodium tartrate and potassium bitartrate mayalso be used. On the basis of starting with 1200 parts by weight ofsalicyclic acid and 400 to 500 parts of hexamine, generally as low asabout 400 to 600 parts up to as high as 1600 to 2000 parts by weight ofpotassium tartrate may be added although for best results about 1000 to1500 parts should be used.

During the performance of the process steps just described, it ispreferred that the potassium hydroxide and tartrate be added as apremixed solution of about 300 to 500 lbs. of potassium hydroxide and600 to 1500 lbs. of water along with about 800 to 1000 up to 1200 lbs.of cream of tartar or potassium tartrate.

While not desiring to be strictly held to a particular theory, it isprobable that formation of one or more of the derivatives of salicylicacid (including the para-amino derivatives) provide the solution withits anode corroding activity and its grain refining and smoothingability. Apparently, as previously indicated, derivatives (ortho andpara) are formed in which the following groups are attached to thebenzene ring of the salicylic acid: amino, carbonyl followed by an aminogroup; NHR and NR where R is preferably methyl or even ethyl or where Ris methylol. Apparently a minor portion of the mixture is p-aminosalicylic acid and it is preferred that only a small portion be thep-amino salicylic acid since it appears that more than 10% of p-aminosalicylic acid 'in the mixture of derivatives provides too active asolution. Thus, the above described reaction condition and process stepsshould be closely followed to obtain a desirable mixture of derivatives.

Generally the amount of water used when the hexamine and salicylic acidare first reacted is about 30 to 90 moles,

and preferably 40 to 60 moles, although, as little as 20' moles or evenas high as 90 to 95 moles or more can be used per mole of hexamine.

In another variation of the process of making the reaction product, theacidic reaction product of salicylic acid and hexamine is reacted with alimited amount of potassium hydroxide, about to 250 lbs. based on .1200lbs. of salicylic acid. Also, unexpectedly, a small amount of hexamineadded before the KOH is added and reacted with the acidic reactionproduct provides an improved catalytic solution. This solution (made byreacting the acidic product with hexamine and the then KOH) is animproved anode corroder, an excellent smoothing and grain refiningagent, and eificiency at the cathode is also improved.

When adding the limited amount of additional hexamine (.05 to 0.3 molebased on one mole of hexamine star-ting material), about 5 to 25 molesand preferably 10 to 18 moles of water is used to make a premixedsolution of the additional hexamine and the limited amount of caustic,namely the 1 to 1.9 moles of KOH or other alkali metal hydroxide.

As before discussed, to help stabilize the resultant solution and toincrease its grain refining activity, generally about /2 to 3 /3 molesand preferably about 1 /2 to 2 /2 moles of potassium tartrate or otheralkali metal tartrate is also added to the solution.

The solution made with the double use of hexamine provides a productimprovement over the process in which salicylic acid and hexamine arereacted at temperatures of 125-190 F. at a pH of 2 /2 to 5 /2 for about16 to 32 hours. At the end of this time, according to the second processjust described, the solution is further reacted with only about 1.2 to1.9 of a mole of KOH in contrast to the former reaction in which 2 to 4moles of KOH are used.

It has been found, surprisingly, that the relatively pure para-aminosalicylic acid does not work well as an anode corroder and a smoothingand grain refining agent; evidently its catalytic action is too greatand violent to make a good addition to a plating bath. However, when itis diluted with unreactedhexamine and some of the paraamino or otheramino derivatives of salicylic acid formed by the above describedreactions, the reaction solution is an excellent anode 'corroder and afine smoothingand grain refining agent.

While the amounts of an anode corroder and a smoothing and grainrefining agent havebeen expressed in ounces per gallon, they may also beexpressed ingrams per liter. Thus, the reaction product of salicylicacid and hexamethylene tetr-amine is preferably present in amounts ofabout 3 to 30 grams per liter.

The following examples are used to illustrate the present invention andnot to limit it in any way.

EXAMPLE 1' A reaction product of salicylic acid and hexamine was made bymixing 1200 lbs. of salicylic acid and 400 lbs. of hexamethylenetetramine (hexamine) in an aqueous solution of 300 gallons or about2'490'lbs. of water. The salicylic acid and hexamine were heated at atemperature of about F. for a period of 24 hours to produce a para-aminoderivative of salicylic acid. The temperature of the reaction was heldwithin 3 of 160 F. at a pH of 4.3 to 4.5.

The batch was vigorously stirred for the first 15 minutes and'thereafterthe reaction allowed to proceed for 24 hours with intermittent stirring.The reaction mixture was allowed to. stand for 24 hours, the 24-hourperiod includingabout 8 hours that the solution took to cool to roomtemperature.

Thereafter, 400 lbs. of potassium hydroxide was added to the solutionwith stirring to bring the pH up to 11 /2 and the reaction continued for8 hours .at 120 F.

The resultant solution was found to be an excellent anode corroder and agood smoothing and grain refining agent for zinc and zinc-alloy cyanideplating baths.

EXAMPLE 2 A zinc cyanide plating bath was made using the followingingredients.

Steel sheets were plated in the above described bath using a bathtemperature of 100 F. and using a current density of 30 amperes per sq.ft. on the anodes. The resultant coating was smooth, evenly distributedthroughout the low and high current density ranges, fine grained and nosandpaper effect was visible. The anodes were smooth and no looseparticles were found to be present.

Steel plates were also plated in a control bath containing all theingredients of the bath just described except for the reaction productof salicylic acid and hexamine. The resultant deposit was uneven, coarsegrained in spots, dull in most areas and generally poor.

EXAMPLE 3 A zinc-copper alloy plating bath was made up using the sameingredients as described in Table 1 except that the cyanide of zinc wasreplaced in part by copper cyanide, there being 6 parts of zinc cyanideand three parts of copper cyanide present in the bath of Example 3,making a total of 9 ounces per gallon of metal cyanide. The platingprocedure employed was similar to that of Example 2, the bathtemperature being 80 F. and the amperage per sq. ft. on the anodes being40. The resultant coating was semi bright, fine grained, smooth and nosandpaper effect was visible. The reaction product of salicylic acid andhexamine was an excellent anode corroder and, as indicated, a finesmoothing and grain refining agent.

EXAMPLE 4 A bath was made up using 8 ounces per gallon of zinc cyanide,5 ounces per gallon of sodium hydroxide, 5 ounces per gallon ofpotassium cyanide and 5 ounces per gallon of potassium bitartrate, and 8ounces per gallon of a reaction product of salicylic acid and hexamine.The reaction product was made as described in Example 1 except 450 lbs.of hexamine was used and the reaction temperature was 170 F. Theresultant coating, when deposited from the bath with a current densityof 40 ASP and a temperature of 150 F. was not satisfactory, the surfacebeing streaked and dull in spots. Apparently there was too muchcatalytic action to form a good zinc coating.

Zinc was deposited from a bath made from the same ingredients as abovedescribed (Example 4) and using the same amounts thereof except that 2ounces per gallon of the reaction product of salicylic acid and hexaminewas used. Again the current density was 40 ASF and the bath temperaturewas 90 F. In contrast to the bath containing 8 ounces per gallon of thereaction product; 7

the bath with 2 ounces per gallon of the catalytic agent produced acommercially satisfactory coating, the coating being smooth and finegrained.

In the above examples, the temperatures of the zinc and zinc-alloyplating bath may be generally from about 68 to 178 F. in order toprovide good coatings. The current density may be varied all the wayfrom slightly aboveO to as high as about 50 amperes per sq. ft. on theanodes.

In the above working examples, equivalent ingredients, as described inthe previous part of the specification, may be used in whole or part forthe ingredients actually used to provide similar results. For instance,sodium hydroxide can be substituted for potassium hydroxide in the bathsshown in Examples 2, 3 and 4. Also, sodium tartrate can be substitutedfor potassium tartrate. In addition, the reaction product made (aspreviously described) from a reaction temperature range from about F. toF. and at a pH of about 2 /2 to 5 /2 and then reacted with alkali metalhydroxide can be used in place of the particular reaction product ofsalicylic acid and hexamethylene tetramine used in the above examples toprovide similar results.

Also, the reaction product of salicylic acid and hexamine made with thedouble use of hexamine and a limited amount of alkali metal hydroxidecan be used as a part or all of the reactionproduct of salicylic acidand hexamine employed in the examples to provide nearly similar results,the above reaction product being a good anode corroder and producingeven a denser plate with improved cathode efficiency.

It is to be understood that other modifications of this invention may bemade without departing from the spirit and scope thereof.

What is claimed is,

1. An aqueous alkaline cyanide plating bath comprising about 3 to 26ounces per gallon of a cyanide of a metal comprising zinc cyanide, about1 to 20 ounces per gallon of an alkali metal hydroxide, about 4 /2 to 26ounces per gallon of an alkali metal cyanide, up to about 7.0 ounces pergallon of an alkali metal tartrate, and about 0.1 to 7.0 ounces pergallon of a reaction product of salicylic acid and hexamethylenetetramine.

2. An aqueous alkaline cyanide plating bath comprising about 3 to 26ounces per gallon of a cyanide of a metal comprising zinc cyanide, about1 to 20 ounces per gallon of an alkali metal hydroxide, about 4 /2 to 26ounces per gallon of an alkali metal cyanide, up to about 7.0 ounces pergallon of an alkali metal tartrate, and about 0.1 to 7.0 ounces pergallon of a reaction product of salicylic acid and hexamine, thereaction being at a temperature of about 125 to 190 F. at a pH of about2 /2 to 5 /2 for at least about 4 hours, and the product thereafterreacted with an alkali metal hydroxide and the final solution having apH of about 8 /2 to 12, said reaction product of salicylic acid andhexamine having the following general formula:

where X is a member of the group consisting of -NH 0 0 H H o -NH, -i:-1I-R I IR and NR where R is a member of the group consisting of alkyl andalkylol.

3. An aqueous alkaline cyanide plating bath comprising about 3 to 26ounces per gallon of a cyanide of a metal comprising Zinc cyanide, about1 to 20 ounces per gallon of an alkali metal hydroxide, about 4 /2 to 26ounces per gallon of an alkali metal cyanide, about 0.01 to 7.0 ouncesper gallon of an alkali metal tartrate, and about 0.1 to 7 ounces pergallon of a solution containing about 0.0009 to 4.7 ounces per gallon ofa derivative of salicylic acid having the following general formula:

Where X is a member of the group consisting of NH 0 law. Add ALB and--NR where R is a member of the group consisting of alkyl and alkylol.

4. An aqueous alkaline cyanide plating 'bath comprising about 3 to 26ounces per gallon of a cyanide of a metal of the group consisting ofzinc .and a zinc alloy, about 1 to 20 ounces per gallon of an alkalimetal hydroxide,

about 4 /2 to 26 ounces per gallon of an alkali metal cyanide, and about0.11 to 14 ounces per gallon of a solution having a pH of about 9 to 12,the solution comprising an alkali metal tartrate, an alkali metalhydroxide and a derivative of salicylic acid which is a reaction productof salicylic acid and hexamine at a pH of about 4.1 to 4.6 and atemperature of about 155 to 170 F. for about 8 to 72 hours to provide areaction mixture and the mixture further reacted with an alkalimetalfhydroxide at about 70 to 190". F. for at least about 4 hours, saidreaction products of salicylic acid and hexamine having the followinggeneral formula:

where is a member of the group consisting of -NH 0 H V t t I NH -N-R N-Rand --NR where R is a member of the group consisting where X is a memberof the group consisting of NH I 'T= .C NR, NR, and -NR where R is amember of the group consisting of alkyl and alkylol. 6.A'n aqueousalkaline cyanide plating bath comprising about 3 to 26 ounces per gallonof copper cyanide and zinc cyanide, about 1 to ounces per gallon of analkali metal hydroxide, about {l /2 to 26 ounces per gallon of an alkalimetal cyanide, about 0 to"7.0 ounces per gallon of an alkali metaltartrate, and about 0.1 to 7.0 ounces per gallon of a reaction productof salicylic acid and hexamine, said reaction product of salicylic acidand hexamine having the following general formula:

where X is a member of the group consisting of NH C-N-R, --NR, and---NR- where R is a member of the group consisting or alkyl and alkylol.

' 7. An aqueous bath for the electrolytic deposition of zinc and zincalloys comprising about 3 to 26 ounces per gallon of a cyanide of ametal of the group consisting of zinc and zinc alloys, about 1 to 20ounces per gallon of sodium hydroxide, about 1 /2 to 26 ounces ofpotassium cyanide, about .0 to 7.0 ounces per gallon of alkali tartrateand about 0.1 to 7.0 ounces per gallon of a solution comprising areaction product of salicylic acid and hexamethylene tetramine, thesolution including a mixture of amino derivatives of salicylic acid andat least some para-amino salicylic acid.'

8. An aqueous bath for the deposition of zinc and zinc alloys comprisingabout 3 to 26 ounces per gallon of a cyanide of a metal of the groupconsisting of zinc and zin a oy of about 1 to 20 ounces per gallon ofsodium hydroxide, about 4 /2 to 26 ounces of potassium cyanide, about0.5 to grams per liter of potassium tartrate,

and about .75 to 53 grams 'per liter of a solutioncomprising a reactionproduct of salicylic acid and hexarnine, the solution including p-aminosalicylic acid, unre tedtiexamin and. unnamed salicylic Midi 9. aqueousalkal aq Wanda P tes t da f elec roly ica ly lat l .19. W allbys' s tbest about 9lll9 PP? gallon f a metal cyanide comprising ginc cyanide,at least about 3 ounces per gal- Ion of go iurn hydroxide,at least about4 /2 ounces per gallon of potassium cyanide, aboUitYS'td 3 ounces pergallon of alkali tartrate and about 0.4 to 4 ounces per gallon or areaction product "of salicylic acid and hexarnethylene tetramine, saidreaction product having the followirig general formula:

OH X I where X is a member the group consisting of NI-l O t 1 -d-NH,il-NR NR and I IR when t is a member of the group consisting r a k l a ilkY b l 10. 'An aqueous alkaline cyanide plating bath adapted forplating zinc and iincalloys comprising abouto' to 2 ounces per gallon ofa 'metal'cyanide'in whichthe'metal includes at least'some z'inc,"about 3to 9 ounces per'gallon of sodium hydroxide, about 10 to 15 ounces pergallon of potassium cyanide, and a't'least' about 0.1 ounce per gallonaqueous solution having apH of about 9fto 12 and containing potassiumtartrate and a reaction product of salicylic acid an hexamethylenetetrainine, the reac tiori product including p-aniin'o salicylic acidand o-an' ino salicylic acidf na' un'r'ea'cted hexamethylenetetrainine'.11'. A method bf makin'g an alkaline cyanide plating bath adapted forelectrodeposition of zinc and zinc-alloys comprising (1) making acatalytic ingredient solution includi g thestepsc iiiflz) reaction about'1 to 4 moles of salicylic acid about 'anamole of 'hexarnine at "atemperature ofiabout to F; and a pH 'of 2 /2 to /2 substantially all thesalicylic acid is dissolved and gassing stopped to provide a reactionmixture and (b) thereafter reacting the'mixture with'an alkali metalhydroxideto provide the catalytic ingredient solution, and (2) mixingabout 0.1 to'7f0 ounces per gallon of said solution withabo'ut3 to 26ounces per gallon of a cyanide of a metal comprising zinc cyanide; about1 to'20 ounces per gallon of alkali metal hydroxide, and up 'to' 7.0ounces per gallon 'ofan alkali metal tartrate' to provide a platingbath.

. method of electrodepositing zinc and zinc alloys comprising the stepsof (1') making an alkalinecy'anid e plating bath adapted forelectrodeposition of zinc and zinc alloys by i) making a smoothing andgrain refining agent solutionineludingrthe steps of reacting about l'tofl moles of salicylic'acid' with' about one mole of hexameth'ylenetetramine at'a 'ternpeiaturc'of about 125 to 190 F. and. aip'H of 2 /2to 5 /2 until substantially all the salicylic acid is dissolved andgassing has stopped to provide a reaction mixture an d (b) thereafterreacting said mixture igvith'an'a'lkalimetal hydroxide to provide thesmoothing and grain refining solution, (2) mixing about 0.1 to 7 .0ounces per gallon of said solution with about 3 to 26 amnesia gallonof acyanide of'a'metal comprising zinc cyanide, about '1 to ZOo'u'n'ces pergallon of an alkali metal hydroxide and up to 7 ounces per gallonof analkali. metal tartrate to form a plating bath, and "(3) electrolyzingsaid batli with a current density of "up toabo'ut 80 amperes per squarefoot 'at'a temperature of about 68to'178F. 7

13, A method of electrodepositing a metal including at least some zinc,the method comprising electrolyzing an aqueous alkaline cyanide solutioncontaining a metal cyanide comprising Zinc cyanide and about 0.1 to 7.0ounces per gallon of a reaction product of salicylic acid and hexamine.

14. An aqueous alkaline cyanide plating bath comprising about 3 to 26ounces per gallon of a cyanide of a metal comprising zinc cyanide, about1 to 20 ounces per gallon or an alkali metal hydroxide, about 4 /2 to 26ounces per gallon of an alkali metal cyanide, up to about 10 7.0 ouncesper gallon of an alkali metal tartrate, and about 1 0 0.1 to 7.0 ouncesper gallon of a reaction product of salicylic acid and hexamine, thereaction being at a temperature of about 125 to 190 F. at a pH of about2 /2 to 5 /2 for at least about 4 hours, and the product thereafterreacted with an alkali metal hydroxide and the final solution having apH of about 8 /2 to 12.

References Cited in the file of this patent UNITED STATES PATENTS2,828,252 Fischer Mar. 25, 1958

1. AN AQUEOUS ALKALINE CYANIDE PLATING BATH COMPRISING ABOUT 3 TO 26OUNCES PER GALLON OF A CYANIDE OF A METAL COMPRISING ZINC CYANIDE, ABOUT1 TO 20 OUNCES PER GALLON OF AN ALKALI METAL HYDROXIDE, ABOUT 4 1/2 TO26 OUNCES PER GALLON OF AN ALKALI METAL CYANIDE, UP TO ABOUT 7.0 OUNCESPER GALLONG OF AN ALKALI METAL TARTRATE, AND ABOUT 0.1 TO 7.0 OUNCES PERGALLON OF A REACTION PRODUCT OF SALICYCLIC ACID AND HEXAMETHYLENETETRAMINE.